1. Field of the Invention
The present invention relates to a method for controlling an index of refraction of silica glass, and more particularly to a method for controlling a refractive index of silica glass wherein only a refractive index of the silica glass in a localized region on the surface thereof may be changed.
2. Related Art
Heretofore, because silica glass, quartz glass, and others, have excellent characteristic properties such as hardness, heat resistance, and chemical stability, in addition to high transmission in a wide range of wavelengths extending from ultraviolet to infrared light, they are often utilized for optical material or optoelectronic material.
Quartz glass exhibits an index of refraction of 1.46 when light having a 633 nm wavelength is irradiated thereon. If the index of refraction of quartz glass can be changed in only a localized area of a surface thereof, then the modified quartz glass may be advantageously utilized for optical material or optoelectronic material. Such modified quartz glass may be used as/in phase shifting devices, light wave-guides, optical integrated circuits, high-density optical memory, and for optical fiber grating.
However, the refractive index of quartz glass cannot be easily changed in only a localized region on the surface thereof. It is difficult to work with and control quartz glass because of its unique physical properties. This creates a problem in producing sufficient amounts of quartz glass having modified refractive indexes, and therefore, limits the amount of quartz glass for use as optical material or optoelectronic material.
There are known ion exchange methods and ion implantation methods useable for changing/modifying an index of refraction of optical materials, such as lithium niobate. Such modified optical materials are used in the devices, and for the applications, discussed hereinabove.
The ion exchange method involves exchanging an ion contained in an aqueous solution with an ion contained in a specific material. The material undergoes a lengthy treatment period (often several hours), which involves immersing the material in the aqueous solution having a very high temperature (around 300xc2x0 C.). This lengthy treatment period is costly and is often difficult to expedite.
The ion implantation method involves implanting an ionized impurity in a specific material. The implanting of the ionized impurity requires the use of highly accelerated energy, which accomplishes the implanting step. However, the ion implantation method increases absorption of the material, which leads to an increase in transmission loss of light. The increase in absorption occurs as a result of damage incurred by the material during the ion implantation process. In addition, both the ion exchange and ion implantation methods require a photolithographic step. The photolithographic step is necessary for forming a minute pattern on/in a treated material.
J. Albert et al. have conducted a trial in which quartz glass was treated by ion implantation in order to change the index of refraction thereof. (J. Albert et al., Opt. Lett. 17, 1652 (1992)). In the trial, Si ion or Ge ion was implanted in quartz glass. The resulting change in the index of refraction (xcex94n) thereof of was 1.2xc3x9710xe2x88x923.
X-ray or gamma ray irradiation has also been used to attempt to change the index of refraction of quartz glass (G. M. Williams et al., Opt. Lett. 17, 532 (1992)). Using this method, the refractive index was modified, but the surface area irradiated with x-rays or gamma rays was darkened significantly. The surface was darkened to the extent that to the naked eye the darkening was discernable. The change in the index of refraction (xcex94n) had an order of magnitude of 10xe2x88x925.
Known phase grating methods achieve a modification in the refractive index having an order of magnitude of approximately 10xe2x88x925.
An object of the present invention is to provide a method for controlling an index of refraction of silica glass, and other materials. The method achieves control of an index of refraction, while concurrently minimizing treatment temperature, treatment time, direct patterning without requiring any photolithographic step. Nonetheless, formation of a minute structure is achievable according to the present invention.
In order to achieve the above described object and other objects of the present invention, provided are methods for controlling an index of refraction of silica glass and other materials. One method includes irradiating a vacuum ultraviolet pulsed laser beam, having the same as or shorter wavelength than a wavelength absorbable by silica glass, to the silica glass to cause photodissociation of a Sixe2x80x94O bond in an area of the silica glass irradiated with the vacuum ultraviolet pulsed laser beam, thereby controlling an index of refraction of the silica glass. A second method includes irradiating a first vacuum ultraviolet pulsed laser beam onto a surface of silica glass, the first vacuum ultraviolet pulsed laser beam having a wavelength shorter than a wavelength absorbable by the silica glass; and irradiating a second vacuum ultraviolet pulsed laser beam onto the surface of silica glass, the second vacuum ultraviolet pulsed laser beam having a wavelength longer than the wavelength absorbable by the silica glass, wherein the irradiating steps cause photodissociation of a Sixe2x80x94O bond in a surface area of the silica glass irradiated with the first and second vacuum ultraviolet pulsed laser beams.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.